Propylene terpolymers are often used in commercial applications due to their desirable impact, rigidity and transparency properties. However, it can be difficult to find an acceptable balance between those properties, particularly when those properties contrast. For instance, compositions exhibiting a certain softness may comprise a high amount of xylene soluble fraction(s) that make them unsuitable for food container applications.
WO 98/58971 discloses a process for producing terpolymers of propylene, ethylene and other alpha-olefins comprising slurry and gas phase reactors connected together using a combination of two or more reactors connected in a cascade for producing a polymer product exhibiting a ratio of ethylene-to-butene of less than 0.3. However, the resulting terpolymer has a low melting temperature and somewhat narrow processing window that may reduce the usability of the polymer.